Two days after a 38-year-old man was killed by a crawler crane that collapsed onto a Lower Manhattan street as workers tried to secure it against accelerating winds, Mayor Bill de Blasio said New York City was lowering the wind-speed threshold at which such equipment must be shut down.

The change, which was to take effect on Monday, was one of several new policies Mr. de Blasio announced on Sunday as investigators worked to determine what caused the fatal collapse and officials faced questions about the city’s protocol for ensuring crane safety.

The new rules would require crawler cranes to stop operating and go into safety mode under two scenarios: when there is a forecast for steady wind speeds of 20 miles per hour or higher or gusts of at least 30 m.p.h., and when actual readings reach those levels. Previously, such cranes could operate until measured wind speeds reached 30 m.p.h. or gusts increased to 40 m.p.h., though individual manufacturers sometimes set stricter standards.

“If at the end of one workday there is a forecast for these kinds of wind levels the next workday, we will require that the crane be put into secure mode the day before,” Mr. de Blasio said. The fine for failing to take appropriate precautions would be increased to $10,000 from $4,800, he said.

The operator of the crane that toppled onto Worth Street in TriBeCa during the morning rush on Friday was working under a 25 m.p.h. limit for securing it, and city officials said workers had begun to lower it as winds neared 20 m.p.h. Mr. de Blasio said forecasts had not indicated that winds would climb above 25 m.p.h. on Friday.

City officials said a preliminary analysis based on recorded wind speeds in Central Park showed that the new standards would have put crawler cranes out of operation on 40 days in 2015. The previous rule shut them down for only seven days.

Officials said the new rules were temporary and would be in place until a task force, to be convened by the mayor, recommended long-term restrictions within 90 days.

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A crane collapsed in Lower Manhattan Friday morning, killing at least one person and injuring several others.CreditCreditStephanie Keith for The New York Times

In the wake of the accident on Friday, the city ordered that 376 currently operating crawler cranes, as well as 43 larger tower cranes, be secured. A National Weather Service forecast predicted wind speeds of 11 to 16 m.p.h. on Monday.

As a further safety measure, uniformed personnel, including police officers, will now help enforce sidewalk and street closings related to crane use, a task previously left to construction crews, with city oversight.

The new policies also call for operators to notify nearby residents and businesses before a crane is moved, as opposed to only when a crane is first installed.

Mr. de Blasio said officials were still evaluating what role wind conditions, human error or structural or equipment problems might have played in the collapse, which sent the crane’s 565-foot boom crashing across roughly two full city blocks.

The crew, in trying to secure the crane and redirect pedestrians away from the area, “was doing exactly what they were supposed to do at that time,” he said.

Three people injured in the collapse have been released from the hospital, Mr. de Blasio said. The crane itself was cut up and removed from the street by Sunday afternoon; some of the surrounding blocks remained closed as workers continued to repair water main leaks.

“We all know there is a construction boom going on in our city,” Mr. de Blasio said. “Although we value the work that’s being done, we value what it means for our economy, we value the jobs that are being created — nothing is more important than the safety of our people.”

Construction executives interviewed on Sunday said that while they were not familiar with details of the new rules, they did not oppose them.

Ross Spivak, president of RES Consulting NYC, which plans to use crawler cranes on a coming project in Manhattan, said while the new regulations could not eliminate all potential dangers, he supported stricter enforcement. “I have no issue with the fines,” he said. “I don’t think it’s smart to take risks.”

A version of this article appears in print on , Section A, Page 18 of the New York edition with the headline: Mayor Announces New Safety Measures After Fatal Crane Collapse . Order Reprints | Today’s Paper | Subscribe